UCL Department of Physics and Astronomy


LHC may falsify Leptogenesis

18 June 2014


From experiments we know that there is an asymmetry of matter and anti-matter in our universe: The excess of baryons over anti-baryons (e.g. protons over anti-protons) could be triggered by a mechanism called leptogenesis, which is currently the most favourite explanation for many particle physicists.

Already in 1967 Sakharov defined three conditions, which such models have to fulfil. One of them is the departure from thermal equilibrium. This is a crucial condition as in thermal equilibrium any net baryon asymmetry produced by a specific process would be immediately destroyed by the inverse process. This is usually called "wash-out".

In this paper Frank Deppisch & Julia Harz (both UCL Physics & Astronomy) demonstrate that it is possible to draw conclusions from observations at the LHC on the evolution of the universe: observing a process which violates lepton number at the LHC is equivalent to establishing a lower limit on the washout factor for the lepton number in the early universe. If the primordial lepton number asymmetry is originally generated above the lepton number violating scale observed at the LHC, the resulting washout will reduce the asymmetry exponentially, rendering leptogenesis ineffective. Thus, the LHC may offer a unique way to rule out leptogenesis.


* LHC: Credits to CERN, under CC BY-SA 4.0 licence [licence, source]

* Spiral Galaxy: Credits to Boris Štromar/ Wikipedia, under CC BY 3.0 licence [licence, source]

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